An example of a conventional brush holder assembly for use in a direct-current electric motor is disclosed in Japanese Utility Model Laid-Open No. HEI 3-18658. The construction of the conventional brush holder assembly will be explained below with reference to FIGS. 4 to 7.
The brush holder assembly comprises a pair of negative-side brush holder frames 2a, 2b and a pair of positive-side brush holder frames 3a, 3b fastened to a base 4.
The base 4 is a steel plate formed into an annulus having a central opening 4a being designed to allow passage of a commutator 1. A plurality of positioning holes 20 are disposed on the base 4. In addition, a plurality of tabs 21 are provided by press working part of the base 4.
Furthermore, the brush holder frames 2a, 2b, 3a, 3b are molded from electrically-insulating synthetic resin.
Brush receiving recesses 22 are disposed in brush holder frames 2a, 3b, respectively, so as to extend from a first end towards a second end without penetrating the second end. Furthermore, pairs of flanges 23 are disposed such that each extends outwards from the bottom end on either side. Fastening slots 24 are disposed on each pair of flanges 23. Furthermore, a lead outlet groove 25 is disposed on one side so as to extend from the first end towards the second end and join the brush receiving recess 22 to the outside. Furthermore, a plurality of protrusions 26 for positioning are disposed on the bottom surface. In addition, a plurality of radiator openings 27 are provided.
On the other hand, brush holder frames 2b, 3a are constructed similarly to brush holder frames 2a, 3b above, except that the lead outlet groove 25 is disposed on the opposite side of each so as to extend from the first end towards the second end and join the brush receiving recess 22 to the outside.
The brush holder frames 2a, 2b, 3a, 3b are fastened onto the base 4 by inserting the protrusions 26 into the positioning holes 20 so as to allow the tabs 21 to pass through the fastening slots 24 and bending the tips of the tabs 21 projecting from the fastening slots 24. At that point, the brush holder frames 2a, 2b, 3a, 3b are fastened to the base 4 such that the open ends of the brush receiving recesses 22 each face the central opening 4a of the base 4 and the axes of the brush receiving recesses 22 pass through the central axis of the central opening 4a of the base 4. By inserting the protrusions 26 into the positioning holes 20, movement of the brush holder frames 2a, 2b, 3a, 3b in the radial direction and in the direction of rotation is controlled. Furthermore, the tabs 21 securing each of the brush holder frames are bent in mutually opposite radial directions, preventing the brush holder frames from dislodging longitudinally.
Negative-side brushes 5a, 5b are inserted into the brush receiving recesses 22 of brush holder frames 2a, 2b, respectively, by passing negative-side leads 7a, 7b through the lead outlet grooves 25. Similarly, positive-side brushes 6a, 6b are inserted into the brush receiving recesses 22 of brush holder frames 3a, 3b, respectively, by passing positive-side leads 8a, 8b through the lead outlet grooves 25. The brushes 5a, 5b, 6a, 6b are placed in contact with the outer circumferential surface of the commutator 1 inserted through the central opening 4a of the base 4 by the force of brush springs 9 disposed within each of the brush receiving recesses 22.
The negative-side leads 7a, 7b connected to the negative-side brushes 5a, 5b are grounded by connection to the base by welding, etc. On the other hand, the positive-side leads 8a, 8b connected to the positive-side brushes 6a, 6b are connected to a power source (not shown) by means of a connector 11. The positive-side leads 8a, 8b are covered with insulating tubing 10 to prevent electrical short-circuiting with the base 4.
This brush holder assembly is mounted onto an end bracket of a direct-current electric motor using screw holes 12 disposed in the base 4.
In the conventional brush holder assembly, as shown in FIG. 4, a negative-side leads 7a passes out of a negative-side brush holder frame 2a in a counter-clockwise direction, and a negative-side lead 7b passes out of a negative-side brush holder frame 2b in a clockwise direction.
On the other hand, a positive-side lead 8a passes out of a positive-side brush holder frame 3a in a clockwise direction, and a positive-side lead 8b passes out of a positive-side brush holder frame 3b in a counter-clockwise direction. In other words, as shown in FIG. 5, the lead outlet grooves 25 in brush holder frames 2a, 3b are disposed in the left-hand side viewed from one end (the front), and as shown in FIG. 6, the lead outlet grooves 25 in brush holder frames 2b, 3a are disposed in the right-hand side viewed from one end (the front).
Thus, two types of brush holder frames having lead outlet grooves in different positions have been used in conventional brush holder assemblies, requiring two types of mold for forming the brush holder frames, and costs could not be reduced. Furthermore, it has been necessary to store the molded brush holder frames separately until assembly is performed. Furthermore, it has been necessary to check the position of the lead outlet grooves and select the brush holder frames during assembly, and there have been cases of operations failure due to incorrect assembly.